A biophysical study is proposed on the response at the lymphocyte plasma membrane level to mitogenic substances and to specific antigen binding in normal and leukemic cells. The cell triggering phenomenon, which is central to the immune response, will be initiated by known mitogenic substances and characterized in physical terms by established biophysical probes of membrane properties. The study will then be extended to specific antigen-binding subpopulations to observe membrane responses to antigen binding and B cell - T cell interactions. In order to achieve the enrichment of cell populations which will be required, a new technique is proposed for sorting large numbers of normal and leukemic cells according to surface specificities. The method (high gradient magnetic separation) depends on providing the lymphocyte subpopulation of interest, with paramagnetic (e.g. ferritin-conjugated) antigens or antibodies against surface markers. Development of the magnetic cell sorting technique will first procede using as the paramagnetic cells erythrocytes which contain some fraction of the hemoglobin iron in a paramagnetic state (ferrihemoglobin or deoxygferrohemoglobin).